I just did a quick search on ZTE WF720. Unless there are multiple versions of the device, the one I found is GSM and WCDMA only. Unless Telus runs a GSM network, I don't think it will work.
About your other questions, if you can port the phone number from Rogers, you will be able to keep the number. There isn't any "home phone" specific plan, so even if the device worked on PM, it will be acting like a mobile phone in itself, except that it is not mobile. So you're better off just keeping your iphone and using it as your primary phone.
The other option that I did when I was with Wind (with poor reception at my house), was to buy a cordless phone bundle (with a base station and 3 handsets) that can connect to your phone via bluetooth. My phone basically sat on a window sill which was one of the only places that got good reception. It would then connect via bluetooth to the cordless phone base station. When I got an incoming call on my cell phone, the cordless phones would ring because it acted like a bluetooth handsfree set. Also, like a bluetooth handsfree set, you could make calls from the cordless phones either through a traditional landline or through your connected iphone. So it's basically like your normal cordless phones except that it can connect to your cell phone as well. This way, you can save $9.99/month.
The cordless set I used is this:
http://www.vtechphones.com/learn/more-vtech/connect-to-cell
What I also did was buy a UPS (uninterruptible power supply) and powered my internet router, cordless phone base station off of it. I bought them when there were on sale but they are powerfull enough to run a computer for 10 minutes. So, you can imagine how long it would last for just an internet router and a cordless phone which draws a fraction of the power. We haven't had many power outages, but I can tell you that when we did, we had Internet and phone service through all of them.
